The present invention relates to crossover filters suitable for dividing wave propagated phenomena or signals into at least two frequency bands.
The phenomena/signals are to be divided with the intention that recombination of the phenomena/signals can be performed without corrupting amplitude integrity of the original phenomena/signals.
The present invention will hereinafter be described with particular reference to filters in the electrical domain. However, it is to be appreciated that it is not thereby limited to that domain. The principles of the present invention have universal applicability and in other domains, including the electromagnetic, optical, mechanical and acoustical domains. Examples of the invention in other domains are given in the specification to illustrate the universal applicability of the present invention.
Crossover filters are commonly used in loudspeakers which incorporate multiple electroacoustic transducers. Because the electroacoustic transducers are designed or dedicated for optimum performance over a limited range of frequencies, the crossover filters act as a splitter that divides the driving signal into at least two frequency bands.
The frequency bands may correspond to the dedicated frequencies of the transducers. What is desired of the crossover filters is that the divided frequency bands may be recombined through the transducers to provide a substantially accurate representation (ie. amplitude and phase) of the original driving signal before it was divided into two (or more) frequency bands.
Common shortcomings of prior art crossover filters include an inability to achieve a recombined amplitude response which is flat or constant across the one or more crossover frequencies and/or an inability to roll off the response to each electroacoustic transducer quickly enough, particularly at the low frequency side of the crossover frequency. Rapid roll off is desirable to avoid out of band signals introducing distortion or causing damage to electroacoustic transducers. Prior art designs achieve rapid roll off by utilizing more poles in the filter design since each pole contributes 6 dB per octave additional roll off. However a disadvantage of this approach is that it increases group delay. An object of the present invention is to alleviate the disadvantages of the prior art.